1. Field of the Invention
The present invention relates generally to automated measurement and inspection apparatus and methods of using same.
2. Description of the Background Art
The measurement of dense lines in integrated circuit technology is rapidly acquiring a more and more relevant role. Such dense features are, for example, are sometimes the target for critical dimension (CD) measurements by CD scatterometry tools. These dense features may often have a one-to-one (1:1) line-to-space aspect ratio. CD scatterometry tools include, for example, a CD scanning electron microscope (SEM).
Unfortunately, the automated measurement of such kinds of structures with a CD-SEM is often problematic, because it can be extremely difficult to distinguish between a line and a trench when the line-to-space aspect difficult to distinguish between a line and a trench when the line-to-space aspect ratio is close to one. This is because the templates for lines and spaces may be very similar in such cases. As a consequence, failures of measuring the intended feature results in erroneous measurement data (flyers) and, consequently, in reduced precision in a critical dimension measurement. Erroneous data may also occur due to operator error, such as, for example, when an operator is setting up a recipe (procedure) and does not recognize proper placement of gates (selected regions) from a top-down view image.
To avoid such erroneous data, a conventional approach locates a target feature to measure by using micro-alignment or pattern recognition. In the conventional approach, a template is used to recognize the feature.
It is desirable to improve CD-SEM and other apparatus which operate using similar principles.